Differential drives are generally known in the motor vehicle industry. Differential drives are used in conjunction with the transmission and drive shaft or propeller shaft (prop shaft) to turn the automotive vehicle wheels at different speeds when the vehicle is going around a curve, in order to differentiate the speed of each wheel individually, and to provide the proper amount of torque to each wheel in slipping, turning, or other road-to-wheel conditions.
In a traditional torque on demand drive train layout of an automotive vehicle there is a primary driven front/rear axle, and a secondary driven “hang on” axle that is connected via a prop shaft or drive shaft and a torque transfer coupling to the primary driven axle. The torque transfer coupling is usually directly in front of and upstream of the secondary driven axle. The axle differential creates the division of power (or torque) to each side shaft of the axle. The primary driven axle can also include a differential which divides necessary power to the side shaft of each front axle shaft and then the wheels. The division of torque between the front and rear axle is completed by the torque transfer coupling which is typically a separate unit on the drive train system and requires space for its housing and other related parts. In a known traditional configuration, a torque transfer coupling for an automotive vehicle is located between the primary and secondary driven axles of the vehicle and, may include a friction clutch pack which is loaded via a ball ramp mechanism. The ball ramp mechanism may be engaged by an electric motor. An electronic control unit senses slip conditions of the wheels, monitors current driving conditions of the vehicle and applies a current to the electric motor which will engage the clutch via the ball ramp mechanism and distribute torque to each wheel as necessary.
An active torque transfer system may provide maximum flexibility in the distribution of torque between the axles of an all-wheel or four-wheel drive automotive system. A similar system can be used in applying torque within an axle on a side-to-side basis between a left rear wheel and a right rear wheel. Other devices currently used in the art for active torque transfer include an electromagnetically engaged pilot clutch to drive a ball ramp mechanism. This mechanism loads the main clutch via electromagnetically engaged pilot clutches. Most of the systems use a ball ramp mechanism but use different engagement mechanisms to engage the ball ramp mechanism to the clutch unit.